At the beginning of the 15th century, in place of a ducal stronghold of wood and earth, a mortar-work structure was built, which with time turned into a royal residence.

The Royal Castle in Warsaw was not the property of the king, but of the state. The king only had his headquarters there and this fact set the Warsaw castle aside from other royal castles in the world. This is also why the castle was called, correctly, ‘the Castle of His Royal Highness and of the Commonwealth.' The king had his official residence in the castle, but at the same time the Sejm of the Commonwealth met there, and the crown officials also worked in the building.